Unable to access instances using floating IP or to reach external router in Red Hat OpenStack Platform

Issue

Unable to access instance VM using floating IP in Red Hat OpenStack Platform. Cannot ping/ssh instances from external network and cannot reach neutron's external router.

The qg- interface of the external router gets configured on br-ex

[root@overcloud-controller-0 ml2]# ip netns exec qrouter-<UUID> ip a
  (...)
25: qr-aaaaaaaa-bb: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1400 qdisc noqueue state UNKNOWN
  (...)
26: qg-bbbbbbb-aa: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1400 qdisc noqueue state UNKNOWN
  (...)

[root@overcloud-controller-0 tmp]# ovs-vsctl show
(...)
    Bridge br-ex
        Port "qg-bbbbbbb-aa"
            Interface "qg-bbbbbbb-aa"
                type: internal
(...)